The present invention relates to an electronic kilowatt hour meter having an improved means for correcting error in the meter.
This invention relates to the metering of electrical energy in terms of, for example, kilowatt hours in an electrical system. Electrical energy in terms of kilowatt hours or kWh has been and continues to be metered with the rotating disc type of meter which is disclosed in, among other sources, the "Electrical Meterman's Handbook", Chapter 7, 7th Edition, published 1965 by the Edison Electric Institute. The invention hereinafter disclosed represents a departure from the methodology and apparatus exemplified by the rotating disc type meter. In addition, those who are familiar with the instrumentation and metering arts respecting electrical power and energy know of proposed systems including apparatus employing electronic and solid state devices for measuring power and energy. An example of such a system is disclosed in Milkovic U.S. Pat. No. 3,951,138 assigned to the common assignee herewith. In such apparatus, the electronic and solid state devices replace the conventional rotating disc. Thus, in prior art systems, the current flowing through a line and the voltage across a load impedance connected to the line are each detected, and signals representing these parameters are coupled to a pulse width amplitude multiplier. The multiplier generates an output signal which is proportional to the product of the detected current and voltage. This signal is then averaged by means of a low-pass filter to provide a DC voltage having an amplitude which is proportional to the total average power of the electrical system. This DC voltage is converted to a pulse train by means of an analog-to-pulse-rate converter, which pulse train has a variable signal repetition rate f which is proportional to the average power in the system, with each output pulse signal representing a constant quantized amount of electrical energy. The output pulse train is then coupled to a display mechanism which may, for example, include a counter or register which performs conventional accumulation, storage and display functions. An example of one such kilowatt hour meter was disclosed in Milkovic U.S. patent application Ser. No. 505,798, now U.S. Pat. No. 3,961,257. None of these electronic prior art metering systems has an internal error correcting means for correcting an offset error within the meter.
It accordingly is an object of this invention to provide a method and apparatus for metering kilowatt hours in a single or polyphase AC electrical system.
It is another object of this invention to provide a method and apparatus for metering kilowatt hours in a single or polyphase AC electrical system wherein error correction is provided in the meter.